Interactive rendering of large scale vector maps is a key challenge for high-quality geographic visualization software systems. In this paper we present a novel approach for the visualization of large scale vector maps over detailed height-field terrains. Our method uses a deferred line shading approach to render large scale vector maps directly in a screen-space shading stage over a terrain visualization. The fact that there is no traditional geometric polygonal rendering involved allows our algorithm to outperform conventional vector map rendering algorithms for geographic information systems. Our flexible clustered deferred line rendering approach allows a user to interactively customize and apply advanced vector styling methods, as well as the integration into a vector map level-of-detail system.